If many South American cities are comprised of straight lines and perpendicular grid systems, then what surely sets Rio de Janeiro apart is its wiggles. Take its skyline. It is a flamboyant signature of crazy shapes - the lopsided M of Sugar Loaf, the exclamation mark of Corcovado, the islands that run out to sea like dots of unfinished sentences. Even the pavements are laid in doodles of black and white mosaic. Some shapes are simple, like the peachy bottoms in tiny bikinis; some are elusive, like the Etch A Sketch puzzle of samba steps. Some shapes have become iconic, like the floating crucifix of its shrouded Christ. Others, such as the haphazard jigsaw of its favela housing, are increasingly on their way to becoming so.

If many South American cities are comprised of straight lines and perpendicular grid systems, then what surely sets Rio de Janeiro apart is its wiggles. Take its skyline. It is a flamboyant signature of crazy shapes - the lopsided M of Sugar Loaf, the exclamation mark of Corcovado, the islands that run out to sea like dots of unfinished sentences. Even the pavements are laid in doodles of black and white mosaic. Some shapes are simple, like the peachy bottoms in tiny bikinis; some are elusive, like the Etch A Sketch puzzle of samba steps. Some shapes have become iconic, like the floating crucifix of its shrouded Christ. Others, such as the haphazard jigsaw of its favela housing, are increasingly on their way to becoming so.

Rio de Janeiro spills over with natural beauty, from the sweeping curves of its golden beaches, to the rainforest that tramples across its mountains. Yet its bays and lagoon are choked with pollution, and for every metre of tropical chic, there are 10 of urban squalor. Rio also boasts some of the worst architecture committed to concrete. But even the most offensive can be forgiven under the swathes of flattering sunlight, which turns to a fabulous pink at dusk.

Everybody should see Rio once, but not only for its postcard charms, or during the mayhem of Carnaval. Really, its main attraction is its infectiously proud and friendly inhabitants - the Cariocas.

Cariocas are happy creatures whose favourite hand gesture is the firm thumbs-up. They are a very watchful people, with men preferring an unblinking stare to the cat-calls of other Latin American cultures, which is always followed by the bum-surveying head-turn.

The Carioca is obsessed with looks, but has little interest in fashion. The exception to this is beachwear. Here the rules are tiny bikinis for girls and crotch-hugging trunks for boys.

Body maintenance is a full-time job and is an entirely public affair. Men work out on the beach. People have no qualms about kindly pointing out that you seem to have put on a few pounds. Women drive to their plastic surgeons in tinted-windowed cars, but openly admit to their Botox top-ups.

Cariocas are obsessive tanners, and seem to think they are immune from skin cancer. The only part they resolutely won't tan is their bikini strap marks; these are worn like proud tattoos of original colouring. People say that beach life is the only truly democratic aspect of Rio, but this isn't true. Look carefully at the quality of bikinis, but more tellingly the skin tone, and you will soon see where the middle-classes go and where the people from the favelas feel more comfortable. The latter are nearly always darker.

The contrast between rich and poor manifests itself in every aspect of life in Rio. Cariocas are famous for being lazy, preferring the pleasures of the beach to performing anything as vulgar as work. This is most often pointed out by the people of Sao Paulo, who are in turn mocked for being workaholics. A popular Sao Paulo joke is that the statue of Christ surveys the city with his arms outstretched because he is desperately trying to spot a Carioca doing a day's work. When that day comes round, he will join his hands together in a slow, sarcastic clap.

Yet, for a city supposedly dedicated to leisure, there are an awful lot of people carrying out back-breaking, Dickensian labour. Barefoot men pull carts piled with rubbish alongside Mercedes on the roads. There is a roaring trade in rubbish in Rio, with hordes of people collecting empty tin cans, politely shaking your beer can to see if it is finished, or rummaging through bins for discarded ones.

There are street children working as shoe-shiners; an odd profession in a place where rich and poor alike mostly wear Havaiana flip-flops. People will try to sell you anything (I know a man who specialises in rabbits, puppies and umbrellas), but are good-natured and splendidly unembarrassed when you point out they have "mistakenly" miscalculated your bill.

Cariocas are very good at eating, but seemingly dreadful at making decisions, which perhaps explains the popularity of kilo restaurants and churrascarias, or barbecue houses. The former are buffets featuring meat, fish and vegetable dishes, as well as the mandatory black beans, which are paid for according to weight. (The fancier ones display calorie content.) The latter are temples to overindulgence and heart disease, in which skewers of barbecued meat are brought to your table, until you eventually give in and place a red "stop" sign over your plate.

The antithesis to all this stodge are the fruit juice bars which are found on every street corner and decorated like Carmen Miranda's head-dress. Many of the fruits consumed here are from the Amazon, and thus have no translatable title in English. But the indisputable king of them is acai, a deep, purple fruit with a gritty-berry-cum-custard taste. It is a child prodigy in terms of vitamin and mineral content, and a perfect accompaniment to inline skating down at Copacabana beach.

The other two Carioca staples are coffee and caipirinha. A cafezinho is called for at all hours of the day, and every possible social occasion. It is taken extremely sweetly, and asking for one without sugar will earn you a suspicious look. The caipirinha is the Brazilian national cocktail. Its ingredients are simple - a high-proof sugar-cane spirit called cachaca, mixed with lime, sugar and crushed ice - its consequences can be less so. Still, alcohol only makes the Carioca even louder and more exuberant - an interesting spectacle - but rarely incites aggression.

Rio is an extremely loud place and only really knows three types of silence, which are all location-specific. They are: in the stands of the Maracana football stadium when the opposing team has just scored (a stunned silence); when an unsuspecting female tourist goes topless on the beach (a disapproving silence); and between the hours of 6am and 1pm on a Sunday (a sleeping silence). *

* The noisiest months in Rio are December to February, during preparations for Carnaval. For all its associations with hedonism, Carnaval is a surprisingly serious business. The samba schools that compete for the championship spend months knee-deep in sequins and constructing the huge, elaborate floats. Rehearsals for the bateria, the deafening, 100-strong drum section are held each Saturday from October, allowing plenty of time for the local community to learn the meandering seven-minute theme song that they repeat as they gyrate down the purpose-built Sambodromo.

Alas, the biggest myth about the Rio Carnaval is that everybody gets to wear buttons on their nipples and a necklace up their bottoms. That's just the soap stars, who also get to teeter on top of the floats. Those who have written down parading in the Rio Carnaval in their "Things To Do Before I Die" list should bear in mind that some people get to dress up as wizards, which can involve a hat with a brim the size of Saturn, a breast plate you couldn't hammer a nail through, let alone whisk a nipple out of, turquoise tights and those awful black pumps forced on British youngsters for PE at primary school.

From a spectator's point of view, the throbbing monsters of the floats can be so overwhelming that they verge on the ridiculous. The participant, however, begins to understand that really Carnaval is less about hedonism, and more of a unified cry for order. The favelas where the samba schools originate are ruled by paramilitary drug traffickers, steeped in gun violence and utterly bereft of public provision. One can't help thinking that Carnaval is a manifestation of Brazil's sadly unrealised potential; that if all the good aspects about this country could operate as smoothly as Carnaval, things would be very different indeed.

Carnaval may only officially run for five days a year, but its spirit pervades the city all year round. It's there when your team scores at the Maracana, as fans samba up and down the aisles to the sound of beating drums. It's there on the pavement bars of a late Saturday afternoon when a group of sambistas strike up an impromptu sing-a-long. It's there at the Sunday barbecues in the favelas, where babies learn to kick their legs in time to samba before learning to walk.

But it is deeply erroneous to suggest that the joys of Carnaval compensate for the misery of many people's lives here. These days, tourists have the option of entering the maze of cubed houses that cling to Rio's hillsides. Favela tours are championed for allowing tourists to get closer to the reality of Rio while contributing directly to the local economy. But such projects are riddled with contradictions, such as the racist undertones of observing the poor from a safari jeep. They are also essentially misleading: until recently one of the most popular tours was of the favela of Rochina, which is the largest shanty town in South America. But since the early hours of Good Friday, it has remained under siege from two warring drug factions. Ten people have been killed and its two million residents are left without water or electricity, unable to leave their homes for fear of being shot. The army is now threatening to occupy the favela, and the tourists have long fled. Meanwhile, life in other parts of the city continues as normal.

Of course, walking through a favela can be exhilarating; there is commerce and initiative, there is beauty and creativity. But none of this warrants the current trend of celebrating favela cool, as demonstrated by the Paris nightclub Favela Chic, or the mock favela bedroom which will soon grace the windows of Selfridges in London. There is certainly a sense of irony to the latter: one of the most noticeable aspects of life in the favela is the complete absence of privacy - which is why they are lined with cheap motels, so people can pay to have sex in private.

Ultimately, though, it is the public nature of the Brazilian experience which makes Rio an unforgettable place. I have never known a city in which it is seemingly impossible to feel alone. And despite its daily tragedies, I have fallen in love with the place. One only hopes that with time - and a decent government - its tragedies cease and its poverty is abolished.

RIO HIGHLIGHTS - BY DAY AND BY NIGHT

BY DAY

Lunch at the colonial cool of Caffe Colombo, in Rio's bustling Centro district.

Taking the tram up to Santa Teresa, and browsing in galleries amid the mansions.

Flirting with the beautiful people in Gavea's ultra-classy night club 00.

TRAVELLER'S GUIDE

GETTING THERE

The only direct flights to Rio from the UK are with British Airways (0870 850 9 850, www.ba.com) which flies three times a week from London Heathrow for around £650, and Varig (020-8321 7170, www.varig.co.uk) also from London Heathrow. You're likely to find the best deals through a specialist agency such as South American Experience (020-7976 5511, www.southamericanexperience.co.uk).

STAYING THERE

The place to stay and be seen in Rio de Janeiro is the Copacabana Palace (00 55 21 2548 7070, www.copacabanapalace.com.br) a wedding cake of a building dripping with 1920s elegance. Rooms start at US$370 (£231). Suites overlooking the pool start at $491 (£307) with penthouses on the executive floor overlooking Copacabana Beach starting at $480 (£300) per night. The breakfast buffet costs an extra $22 (£14) per person, but those on a more limited budget should at least sip a gin and tonic at the poolside bar.

A cheaper option is the Arpoador Inn (00 55 21 2523 0060) which is the only hotel in the area situated directly on the beach. Prices start at around Brazilian Reais 363 (£70) for a double room with a sea view per night, including breakfast.

Beachwear, flip-flops and diamonds are the best buys in Rio. For bikinis, head to Salina, Bum-Bum and Osklen, which all have stores in Rio Sul, the unsightly shopping mall in between Copacabana and Botafogo. A good bikini will set you back about £30. Havaianas flip-flops are ubiquitous, though you'll have to go to the jeweller H Stern (00 55 21 2259 7442, www.hstern.com.br) at Rua Visconde de Pirajá 490 in Ipanema if you want the diamond-encrusted variety.

GETTING AROUND

Local buses are fast, frequent and cheap, but beware of thieves who operate on them. The underground metro is excellent, but only for trips from Copacabana to the centre or Maracana. Taxis are reasonable, but don't expect the drivers to speak English, and make sure they set the metre.

EATING OUT

For an excellent traditional Brazilian meal of grilled chicken, farofa (manioc flour) and rice, head to Braseiro on Praça Santos Dumont in Gávea. Baby Launches on Constante Ramos in Copacabana is an excellent fruit juice bar whose empanadas and pastries are legendary.

For something different, try Mala e Cuia on Barata Ribeiro in Copacabana, a self-service buffet of the meat-heavy food from neighbouring state Minas Gerais. All of the above will fill you up for less than BR52 (£10), the latter two for less than BR26 (£5).

Zaza Bistro on Prudente de Morais in Ipanema is one of Rio's most stylish restaurants with a menu combining Caribbean, French, Thai and North African tastes. Expect to pay around BR157 (£30) for three courses with wine.

FURTHER INFORMATION

Riotur is the city's tourist agency, with a tourist centre located in Copacabana at Avenida Princesa Isabel 183 (00 55 21 2541 7522), which is open daily from 9am-6pm Monday-Friday.

In the UK, The Embassy of Brazil (020-7399 9000, www.brazil.org.uk) can offer tourist advice.